1. Field of the Invention
The present invention relates to a vacuum fluorescent display driving apparatus. The present invention particularly relates to a driving apparatus employed with a vacuum fluorescent display having plural grid electrodes and anode electrodes.
2. Description of the Related Art
Vacuum fluorescent displays are employed as display elements for displaying an image. Vacuum fluorescent displays discharge electrons from a filament, and accelerate the discharged electrons by selectively applying voltage to grids and anodes, such that the electrons are irradiated onto fluorescent body provided to an anode.
A controller driver for vacuum fluorescent displays is described in Japanese Patent Application Laid-Open (JP-A) No. 2002-40991 having an object of reducing cost and increasing the degrees of freedom for design in this type of conventional vacuum fluorescent display. This vacuum fluorescent display controller driver includes Random Access Memory (RAM), a grid driver, an anode driver and a control section. The RAM stores display data input from outside. The grid driver scans the vacuum fluorescent display. The anode driver drives specific display segment electrodes. The control section supplies a driver signal to the grid driver and the anode driver. The control section includes a simple grid control section that simply scans the vacuum display, and a universal grid control section that enables plural grids to be selected at the same time. The control section repeats, a simple scan mode for simply scanning the grid, and a universal scan mode that selects and scans plural electrodes, according to a display pattern of the vacuum fluorescent display.
A display controller driver is described in JP-A No. 4106771 that facilitates diversity in display content. This display controller driver includes an interface, a decoder, display RAM, a grid driver, an anode driver, a control section and a timing generator. The interface performs transmission and reception of data with to and from a host computer. The decoder decodes command data and display data that has been input from the interface. The display RAM stores display data that has been separated by the decoder. The grid driver and the anode driver drives the display section based on the display data stored in the display RAM. The control section sets the driving method of the display section based on command data, and also reads out display data corresponding to this driving method from the display RAM. The timing generator supplies a timing signal to the interface, the decoder, the display RAM, the grid driver, the anode driver and the control section for setting the operation timing thereof. Grid data for forming a scanning signal corresponding to the driving method of the display section, and anode data corresponding to the display data, are stored in the display RAM. Each of these types of data are read out according to specific timing address, and are supplied to the anode driver or the grid driver via a latch circuit.
However, in the technologies described in JP-A No. 2002-40991 and JP-A No. 4106771, when a segment straddling plural grids is illuminated, driving power needs to be supplied simultaneously to plural grid electrodes connected to the plural grids. Accordingly, as the number increases of grid electrodes to which power is to be supplied simultaneously, excessive current flows in the power lines of the grid driver employed for driving. This results in a deterioration and/or melting and breaking of the power lines. Whilst the above can be rectified by increasing the thickness of the power lines, if the thickness of the power lines is simply increased this leads to a corresponding increase in size of the apparatus.
The above does not only occur in relation to the grid driver, but also occurs in relation to the anode driver.